The euro will soon be a familiar sight to millions of Britons despite the UK's decision not to join, according to a pro-euro campaign group.

The introduction of the single currency will have a "massive impact on the people of Britain", a Britain in Europe spokesman told BBC News Online.

I'm in favour of the euro and I'm sure once we're all used to it Britain will have to adopt it

Holidaymaker David Sharpley

He said up to 40 million business people and holidaymakers will use euros this year when they travel to one of the 12 countries which have adopted it as their official currency as of Tuesday.

Some high street shops in tourist areas in the UK, such as Debenhams and Marks and Spencer, have said they will accept the currency alongside pounds.

On New Year's Day the first transactions had already begun.

Tourist trade

The campaign group Britain in Europe said even those with no holiday plans would soon see the new currency.

Holidaymakers are getting their currency in euros

Campaign members started the New Year by handing out dummy euro notes to shoppers on London's Oxford Street, where one in three shops have already said they will accept the currency.

A spokesman said: "I don't think you should overestimate how many will spend euros in Britain.

But he continued: "If tourists are going to come here and want to spend euros it's difficult to see how shops will be able to say 'no'."

But a spokesman for the anti-euro No campaign downplayed the significance of the development.

"Don't believe the hype
- the euro is not going to spread like a virus through the British economy. The fact that some shops will accept the euro shows that we can have the best of both worlds," James Frayne told BBC News Online.

Reporting from Oxford Street, the BBC's Dharshini David said there was little sign on Tuesday of shops advertising that they were accepting the euro.

But she said for those shops that were accepting this currency this was little different from them already accepting foreign currencies like the US dollars.

On Tuesday travellers from airports across Britain were coming to terms with the currency changes.

Bureaux de change reported that almost all customers travelling to the eurozone opting for it instead of the traditional currencies.

Debbie Moorhouse, manager of Travelex in Heathrow airport's Terminal One, said: "It's a fairly quiet day of the year for us, but we've done quite a
bit of business so far in the euro.

"You can still get the old currencies for a short while if you want them, but we are advising customers to take out euros as they will get their change in euros if they pay in the previous currency."

Currency cost

Most of those flying to Europe from Heathrow welcomed the change, despite a few nerves.

Father-of-three, David Sharpley, who was heading to Rome with his family, said he hoped the changeover would not be too complicated.

Mr Sharpley, 44, from Oxford, said: "I'm in favour of the euro and I'm sure once we're all used to it Britain will have to adopt it.

"But for this holiday we will still be converting everything we buy from euros, to lira and then to pounds to understand how much it costs."

James Shock, 41, a Briton who had moved to Chicago with his wife and two children, said he liked the look of the notes.

He said: "They are a bit like the Dutch guilder. They are nice colours and different sizes so they should be fairly easy to use once you get used to their worth."

At Newcastle Airport pro-euro campaigner Hugh Morgan Williams was one of the first to spend his notes.

Mr Williams, chairman of the North East in Europe pressure group, bought his three-year-old daughter Keira a packet of sweets at WH Smith's, one of many airport outlets accepting euros.